Gasification processes are widely used to convert solid or liquid feedstocks such as coal, petroleum coke and petroleum residue into synthesis gas (syngas). Syngas is an important intermediate feedstock for producing chemicals such as hydrogen, methanol, ammonia, synthetic natural gas or synthetic transportation oil, or as a fuel gas for power generation.
A common practice for gasification processes is to recycle unreacted char back to the gasification reactor using a complex system of lock-hoppers, which generally includes multiple vessels connected in series, where each vessel can be individually pressurized and de-pressurized. These systems are typically used for transferring solids from a low pressure to a higher pressure environment. However, because of the frequent cycling and batch operations, lock-hoppers are very maintenance intensive, contributing to the high cost of operating such a system. In addition, there is a higher capital cost associated with the use of multiple vessels, valves, and instrumentation. Gas consumption, recycling, and management for pressurization and de-pressurization of the lock-hoppers is an additional factor for consideration.
As an alternative to lock hoppers, rotary valves have also been used for transferring solids from a low pressure environment to a higher pressure environment. However, high erosion wear in the rotor, especially for applications involving fine abrasive solids like char, is a serious problem.